U.S. Pat. No. 6,209,475 describes an anchor device wherein the connecting member between the anchor and its anchor line can be opened by interaction between one or more pistons, movable radially on the connecting member, and a bell-shaped body which can be lowered along the anchor line in order to interact with these pistons.
The pressure exerted as a result of the insertion of the bell into the connecting member causes the release of the latter and the consequent disconnection of the anchor line from the ring of the anchor. However, a connection is maintained by means of a retrieval line which connects the connecting member to the crown of the anchor.
This solution enables the anchor to be retrieved in case of fouling, and, if the retrieval line is weaker than the anchor line, it enables at least the latter to be retrieved as a result of the breaking of the retrieval line if it proves impossible to free the anchor. However, this solution has two main drawbacks. The first is that the piston causing the connecting member to open is movable radially with respect to the axis of the member, and therefore the piston moves orthogonally to the direction of sliding of the bell used for the opening operation. Because of the hydrostatic pressure acting on the bell, the opening operation may be difficult in the presence of grains of mud or sand which impede the movement of the piston. Secondly, the device is subject to potential accidental opening of the connecting member between the anchor and the anchor line, due to interference between the connecting member and rocks on the sea bed. In practice, there is no protection for the piston which causes the connecting member to be released. Furthermore, the device, at least in the solution shown in FIGS. 9 and 10 of U.S. Pat. No. 6,209,475, is resiliently stressed towards an open condition the connecting member, which is somewhat hazardous because of the aforementioned risk of accidental release.
U.S. Pat. No. 2,669,962 describes an anchor device whose release, when the anchor has become fouled, is dependent on a sudden pull on the anchor line. Since sudden pulls may also occur as a result of powerful atmospheric disturbances, the system is insufficiently reliable.
There are also known anchor devices which include a retrieval line associated with a sleeve which is slidable on the anchor line and which can be hooked from above, if the anchor becomes fouled, so that a pull can be exerted on the retrieval line. These devices (see, for example, www.anchorrescue.com) have the drawback that, if the anchor becomes fouled, it is recovered purely by using the line associated with the retrieval line, rather than by using the anchor line. In critical conditions, as in the case of a squall, the pull exerted in this way may be excessive. Furthermore, if the release operation is unsuccessful, there is a risk that the anchor line may be lost as well as the anchor.